1. Field of the Invention
The present invention relates to a pump for use in biomedical systems, for example as a drug dispensing pump implantable within a human body. More particularly, the invention relates to such a pump utilizing a thermally responsive diaphragm as a component of the pump chamber and operable to alternately load and then completely empty the chamber, through valve controlled inlet and outlet passageways, in a regulated manner for, as an example, periodic dosing or dispensing of a medicament.
2. Description of the Prior Art
Heretofore, various pumps have been proposed wherein the pumping action is derived from a flexing diaphragm with, in many instances, the motivation for the pumping action being derived from a thermal differential. Several of these known pumps are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. PATENTEE ______________________________________ 2,867,224 Martiniak et al 2,884,866 Patterson 3,152,554 Kofink 4,152,098 Moody et al 4,204,538 Cannon 4,231,720 Konig 4,265,601 Mandroian 4,411,603 Kell ______________________________________
The Martiniak et al U.S. Pat. No. 2,867,224 discloses a conditioning dispenser for use in a washing machine wherein an enlarged pumping chamber is communicated, through a check valve, with the interior of a vented liquid container. The pump chamber also communicates with a washing vat through an elongated valved outlet passageway. Movement of liquid into and out of the pumping chamber is effected by the snap flexing of a bimetallic disc selectively heated by a remote resistance heater designed to have substantial thermal output to overcome appreciable heat loss from the disc into the liquid in the large pump chamber. The disc, when heated, snaps inwardly relative to the pump chamber and dispenses a predetermined minor portion of the liquid therein. The bimetallic disc forms a minor portion of the bounding wall of the pump chamber and, in its inwardly drawn dispensing position, does not conform to the interior of the chamber, does not fully dispense the contents thereof, and does not seal against the chamber communicating ends of the inlet and outlet passageways.
The Patterson U.S. Pat. No. 2,884,866 discloses a fluid pump wherein the pumping action, through valved inlet and outlet passageways, is effected by a tubular elastic body surrounded by a thermal responsive expansible-contractible material incorporating an electric heating element for a selective heating of the material and a corresponding contraction of the cavity within the elastic body and a forcible discharge of liquid therein.
The Kofink U.S. Pat. No. 3,152,554 discloses a variety of systems wherein thermally responsive bimetallic elements effect a mechanical movement of pump diaphragms, switches and valves. In one instance, reference is made to the possibility of utilization of the bimetallic element proper as an electrical resistance conductor which is heated when current flows through it. There appears to be no indication of the bimetallic member itself constituting a material pumping diaphragm.
The Moody et al U.S. Pat. No. 4,152,098 discloses a micropump which can be implanted in a patient's body for the controlled delivery of pharmaceuticals or the like. The pump utilizes a diaphragm which is selectively flexed by the electromagnetic actuation of a plunger for selective movement of a portion of the diaphragm into and out of the pumping chamber. Movement of fluid through the inlet and outlet is controlled by a valving action utilizing the diaphragm itself which extends in overlying relation to each of the ports. The diaphragm in flexing under the influence of the separate plunger, does not conform to the wall of the pumping chamber.
The Cannon U.S. Pat. No. 4,204,538 discloses a cassette for the controlled introduction of intravenous fluid into a patient utilizing flexible diaphragms as valving means and as a means for directional control of the flow through first and second compartments defined within a chamber by a central diaphragm. The diaphragms provide no pumping action.
The Konig U.S. Pat. No. 4,231,720 discloses, in the embodiment of FIGS. 3 and 4, a membrane which, through mounted bimetallic strips, flexes between two chambers in response to temperature differential in the liquids within the chambers to effect a movement of fluid into and out of the chambers through appropriate check valves.
The Mandroian U.S. Pat. No. 4,265,601 discloses pump apparatus, for possible use in medical applications, wherein a diaphragm bifurcates the pump chamber into a first chamber volume which receives the pumped fluid and a second chamber volume containing a pumping fluid. A remote electrical heater heats the pumping fluid causing an expansion of this pumping fluid which in turn causes the diaphragm to expand against the sides of the pump chamber and thereby expel all of the pumped fluid from the first chamber volume. This system requires a separate enclosed heating chamber and the utilization of an expandable pumping fluid.
The Kell U.S. Pat. No. 4,411,603 discloses a blood pump incorporating a flexible diaphragm selectively expanded into a pumping chamber by a reciprocating plunger or piston. Flapper valves control the flow to and from the chamber.
As will be described in detail subsequently, the pump of the present invention differs from previously proposed pumps by providing a pump particularly for use within a biomedical environment and wherein the pump chamber is partially defined by a diaphragm composed of a bimetallic disc responsive to direct electrical resistance heating for a fluid pumping movement of the diaphragm resulting from a differential thermal expansion of the bimetallic components of the disc.
The diaphragm is so related to the pump chamber as to effect a full expulsion of the contents of the chamber upon a cooling of the diaphragm and a movement of the diaphragm from its thermally expanded position to its cooled at rest position. The pump chamber, in the absence of a cycling of the pump through a direct heating of the bimetallic diaphgram, is empty of fluid.